The invention relates to stabilized amido acid compositions. More particularly, the invention relates to compositions of amido acids, such as 6-nonanoylamidohexanoic acid, stabilized with antioxidants. The stabilized amido acid compositions are useful in the manufacture of bleach activators such as sodium nonanamidohexanoyloxybenzenesulfonate. Stablization of the amido acid protects chemical degradation. Additionally, bleach activators made from the stabilized amido acids of the invention possess improved color.
Hypochlorite and hydrogen peroxide are well known for their bleaching properties. As a bleaching agent in laundry detergents, hydrogen peroxide has the advantage of being safe to use with many fabric dyes. However, hydrogen peroxide bleaches are not effective at temperatures below 50xc2x0 C. This limits their use as most laundering is carried out at temperatures below about 40xc2x0 C. For this reason, various peroxyacids were developed as alternative bleaching agents for use in laundry detergents. The peroxyacids were generally found to be effective bleaching agents at the lower laundering temperatures. Because of their chemical instability and potential safety hazards, however, peroxyacids themselves are generally unsuitable for storage and handling.
Bleach activators were developed to address storage and handling concerns associated with peroxyacids. Bleach activators have the ability to hydrolyze under laundering conditions, effectively producing peroxyacids, even at lower temperatures, e.g. below 40xc2x0 C. By perhydrolyzing bleach molecules, bleach activators enhance the activity, and thus the cleaning ability, of a laundry detergent. Bleach activators have the further advantage of being stable when stored in solid form at room temperature. These properties permit the use of bleach activators in a wide variety of laundry detergents and other cleaning formulations.
An important class of bleach activators is phenyl ester salts. An effective bleach activator, phenyl ester salts readily react with bleach to form the corresponding peroxyacid. Exemplary phenyl ester salts, which are used as bleach activators, and their preparation are described in U.S. Pat. Nos. 4,634,551; 4,852,989; 5,391,780; 5,393,905; 5,393,901; 5,414,099; 5,466,840; 5,523,434; 5,650,527; and 5,717,118; as well as in published PCT applications WO 94/18159, WO 95/07883, WO 96/16148, and WO 99/09004. These U.S. patents and published PCT applications are incorporated herein in their entirety.
Bleach activating phenyl ester salts can be prepared in various ways. For example, sodium nonanamido-hexanoyloxybenzenesulfonate can be prepared by reacting a C9 fatty acid, and caprolactam to form 6-nonanoylamidohexanoic acid. Sodium p-hydroxy-benzenesulfonate and acetic anhydride are then reacted with the nonanoylamidohexanoic acid (an amido acid) in a solvent to form sodium nonanamidohexanoyloxybenzenesulfonate. This reaction mechanism is shown below in equations 1A and 1B. 
The major difficulty with such a reaction is the formation of unwanted colored by-products. As such, the final product can possess a commercially undesirable non-white appearance. The formation of these non-white, colored by-products are believed to be due in large part to the oxidation of the amido acid intermediate formed during the process. Such an oxidation process may be similar to the oxidation of N-alkylamides, as described by Sager: M. V. Lock and B. F. Sager, J. Chem. Soc. (B), (1966), 690, B. F. Sager, J. Chem. Soc. (B), (1967), 428, and B. F. Sager, J. Chem. Soc. (B), (1967), 1047. Oxidation of the amido acid intermediate causes the formation of unwanted color as well as chemical degradation of the amido acidxe2x80x94both of which are undesirable.
The removal of unwanted colored by-products from the commercial phenyl ester salts is difficult and expensive. Indeed, current techniques for removing color from phenyl ester salts, such as sodium nonanamidohexanoyloxybenzenesulfonate, either fail to produce a colorless, commercially desirable, white product or require undue time and/or expense. For example, one technique used in forming amido acid phenyl esters involves sparging an inert gas through the amido acid reaction system. See, for example, U.S. Pat. No. 5,414,099. Another technique which has been described involves admixing a water-based purification system with an amido acid phenyl ester sulfonate reaction product to form a purification system and separating the purified phenyl ester salt from the purification system such that a percentage of the color forming impurities are removed. See, for example, published PCT Application WO 99/09004.
Accordingly, there is a need in the art for a simple, cost-effective means of forming precluding or lessening the formation of colored by-products during the synthesis of phenyl ester salts.
The invention answers the problems connected with forming substantially discoloration-free phenyl ester salts, which may be used as bleach activators. More particularly, commercially acceptable amido acids for use in the formation of bleach activating phenyl ester salts generally appear white and do not contain discolored amido acid by-products. By employing white amido acid products in the preparation of phenyl ester salts, a commercially acceptable phenyl ester salt can be prepared.
The invention aids in the prevention of discoloration and chemical degradation by providing stabilized liquid amido acid compositions. More specifically, the invention provides a stabilized liquid amido acid composition which contain at least one amido acid and an antioxidant. Additionally, the invention relates to processes of making a stabilized amido acid composition as well as processes for preparing an amido phenyl ester salt from an antioxidant stabilized amido acid.